The determination of the rotational state and interior structure of Venus using VERITAS radar tie points

Abstract:

VERITAS (Venus Emissivity, Radio Science, InSAR, Topography And Spectroscopy) is a Discovery mission proposal addressing the many open questions regarding Venus structure and evolution. Among the main scientific objectives of the gravity/radio science experiment, the determination of the rotational state of Venus stands out since the inertial motion of the rotational pole is directly related to the principal moments of inertia and has never been directly measured. The high accuracy measurement of the body-fixed gravity field enables a precise determination of the spin vector of the planet, and thus of its precession rate and polar moment of inertia. A different method to access the rotational state of the planet is based on radar observations of surface landmarks. VERITAS hosts an interferometric synthetic aperture radar that will provide the most precise global mapping of the surface of Venus. The VERITAS orbital geometry is designed to produce a repeating ground-track every 245 days, allowing to revisit the same regions with the same observation path 4 times during the nominal mission duration. These observation conditions enable the identification of surface landmarks in multiple acquisitions and to track their positions over a broad time span, providing independent and additional information on the rigid body orientation of the planet. In this work we investigate the possibility of a combined data processing strategy of gravity Doppler data and repeat radar landmark measurements (tie points) in a unified framework. The inclusion of repeat landmarks observations over adjacent orbits and multiple revisit cycles proves to be an effective addition to the gravity dataset allowing a more precise determination of the spacecraft trajectory and, as a consequence, a finer estimation of the physical parameters of interest to the knowledge of the interior structure of Venus.